Sifting or settling apparatuses generally include a material feed device, material support unit with holes through which flows a gaseous fluid, often gas guided by a plenum disposed underneath the material support unit, and a discharge control mechanism for controlling separated discharge of relatively heavier material and relatively lighter material. The inflowing pulsed gas operating to loosen the material fed onto the material support unit stratifies the material into layers of relatively lighter material atop of layers of relatively heavier material. An air sifting apparatus of this type is described, for example, in the publication Schubert “Aufbereitung fester mineralischer Rohstoffe”, Band II VEB Deutscher Verlag fuer Grundstoffindustrie, Leipzig, pages 89 and 90.
Typically, sifting apparatuses, like the one described above, produce a less distinct separation between the heavier and lighter materials when compared with wet sifting machines. To achieve satisfactory sorting results according to the aforementioned apparatuses, traditionally multiple factors must be present including, for example, a large density difference between the components of the material. The material particles must be classified within a relatively narrow size range (i.e., within a narrowly defined kernel or grain size range), and the surfaces of the particles should be low in surface moisture, otherwise capillary retention forces hinder their relative movement.